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Probing ultralight axions with the 21-cm signal during cosmic dawn

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Selim C. Hotinli, David J.E. Marsh, Marc Kamionkowski

Original languageEnglish
Article number043529
JournalPhysical Review D
Issue number4
Accepted/In press8 Aug 2022
Published23 Aug 2022

Bibliographical note

Funding Information: S. C. H. thanks T. Binnie and J. B. Muñoz for useful conversations. S. C. H. is supported by the Horizon Fellowship from Johns Hopkins University. D. J. E. M. is supported by an Ernest Rutherford Fellowship from the Science and Technologies Facilities council of the United Kingdom. This work was performed in part at Aspen Center for Physics, which is supported by National Science Foundation Grant No. PHY-1607611, and a grant from the Simons Foundation. This work was supported at JHU in part by the Simons Foundation and by National Science Foundation Grant No. 2112699. Publisher Copyright: © 2022 American Physical Society.

King's Authors


Ultralight axions (ULAs) are a promising and intriguing set of dark-matter candidates. We study the prospects to use forthcoming measurements of 21-cm fluctuations from cosmic dawn to probe ULAs. We focus in particular on the velocity acoustic oscillations (VAOs) in the large-scale 21-cm power spectrum, features imprinted by the long-wavelength (k∼0.1 Mpc-1) modulation, by dark-matter-baryon relative velocities, of the small-scale (k∼10-103 Mpc-1) power required to produce the stars that heat the neutral hydrogen. Damping of small-scale power by ULAs reduces the star-formation rate at cosmic dawn which then leads to a reduced VAO amplitude. Accounting for different assumptions for feedback and foregrounds, experiments like HERA may be sensitive to ULAs with masses up to mα≈10-18 eV, two decades of mass higher than current constraints.

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